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DTC's

R

Rodd

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Antelope, CA
I have a couple codes on my suburban. P0126 Insufficient coolant temp and P0236 Turbo Boost sensor A circuit range.

The coolant temps sensor is plugged in so it may be bad (Front of engine on driver side below head and A/C), however there is a plug that shares the same wiring harness as the plug that goes into the temp sensor that is unplugged and I cant figure out where it goes. Is there a plug that goes into the brake master cylinder? I don't think so. The reason I ask is I replaced it a while ago with an upgraded one from a duramax that has a plug but this plug doesn't fit.

I have deleted the vac pump for the turbo years ago and haven't had the code until now. I did plug the black hose and just noticed the red plastic hoses have come out that may be the issue. Take a look at the pictures below.
 
Here are the pictures.
 

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The sending unit at the front of the left side head is for the temperature gauge.
The temp sensor that reports low coolant temp to the computer(ECM) is located on the thermostat cross over assembly, where the upper radiator hose comes out of the engine. It will have a two prong plug that goes into it, like the one in the pic.
The boost DTC is caused if the turbo boost is too high or to low for what the ECM deems is necessary for proper performance of the engine.
What year model, transmission of a truck is this ?
 
MrMarty51 said:
The sending unit at the front of the left side head is for the temperature gauge.
The temp sensor that reports low coolant temp to the computer(ECM) is located on the thermostat cross over assembly, where the upper radiator hose comes out of the engine. It will have a two prong plug that goes into it, like the one in the pic.
The boost DTC is caused if the turbo boost is too high or to low for what the ECM deems is necessary for proper performance of the engine.
What year model, transmission of a truck is this ?
Click to expand...
98 k2500 suburban Auto trans
 
So the sensor could be bad but I need to find out where that plug goes just in case it is related and causing the code.
 
Jaryd said:
Im not at my truck to look right now but I think that the crank position sensor is at the end of the coolant sensor harness
Click to expand...
I think You are correct, IIRC, the plug on mine is behind or below the AC compressor. It too is a two wire plug.
Also, if that wire is long enough to reach the lower back of the PS pump can, it might be that the variable orfice valve on the back of the PS pump has been eliminated and the harness plug laid out to the wind. 🤷‍♂️
 
Rodd said:
So the sensor could be bad but I need to find out where that plug goes just in case it is related and causing the code.
Click to expand...
Try, the variable orifice at the P/S pump...like Marty pointed out...GM ha a kit to eliminate that valve and vehicles using hydro winch had to eliminate it too...like I did.
Boost sensor wire if broken in the harness on fire wall will not allow timing to be set on the 99 Burb "I had this problem some years back".
 
Am surprised that the truck is not shifting funky. When the Burb's ECT sending unit in the crossover started to fail, the ECM commanded TCC unlocks and downshifts in an apparent attempt to warm the motor when the computer thought that the coolant was too cool.

Replacing the crossover ECT sending unit is fairly easy. Warm the system up a bit (not a lot, but enough that there is pressure in the system), shut off the motor, open the coolant reservoir cap to release pressure, reinstall the cap, and let the system cool back down which will develop a slight vacuum in the coolant system. Once the system is cool, replace the sending unit. With negative pressure inside the coolant system, should not have much (if any) coolant loss during the parts swap.
 
MrMarty51 said:
I think You are correct, IIRC, the plug on mine is behind or below the AC compressor. It too is a two wire plug.
Also, if that wire is long enough to reach the lower back of the PS pump can, it might be that the variable orfice valve on the back of the PS pump has been eliminated and the harness plug laid out to the wind. 🤷‍♂️
Click to expand...
That is probably it. I (My son) replaced the PS pump about 1 1/2 months ago.
 
FellowTraveler said:
Try, the variable orifice at the P/S pump...like Marty pointed out...GM ha a kit to eliminate that valve and vehicles using hydro winch had to eliminate it too...like I did.
Boost sensor wire if broken in the harness on fire wall will not allow timing to be set on the 99 Burb "I had this problem some years back".
Click to expand...
What portion of the firewall is the boost sensor located?
 
JayTheCPA said:
Am surprised that the truck is not shifting funky. When the Burb's ECT sending unit in the crossover started to fail, the ECM commanded TCC unlocks and downshifts in an apparent attempt to warm the motor when the computer thought that the coolant was too cool.

Replacing the crossover ECT sending unit is fairly easy. Warm the system up a bit (not a lot, but enough that there is pressure in the system), shut off the motor, open the coolant reservoir cap to release pressure, reinstall the cap, and let the system cool back down which will develop a slight vacuum in the coolant system. Once the system is cool, replace the sending unit. With negative pressure inside the coolant system, should not have much (if any) coolant loss during the parts swap.
Click to expand...
The truck shifts just fine. Thanks for the replacement procedure. Just to confirm, the coolant switch is the one under the A/C and behind the PS pump on the block?
 
The boost sensor is on the intake. The ECT sensor on the block is for the dash gauge. The one the PCM reads is on the coolant crossover near the thermostat
 
Rodd said:
What portion of the firewall is the boost sensor located?
Click to expand...
It wire goes into the big fat harness on the firewall from the boost solenoid unit bolted to the intake, I just ran a wire from it to the proper pin on ECM, "however do not forget to clip the wire from the ecm to the boost solenoid leaving enough for you to tap into ecm. I did this instead of messing with the harness, reason is the harness wire insulation maybe melted in spots for heat and age "MINE WAS".
 
Thanks guys! I'm less worried about the boost code because I do have the waste gate controller turned up just a little where occasionally it will throw a code. I think that is a stored code. The other one is the more important one.
 
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